As those of ordinary skill in the art will understand, many modern water craft include an array of sensors for detecting various conditions of the engine, engine components, and the watercraft. An engine controller can use output signals from the sensors to control engine operation. The sensors can include a sensor that detects a condition of the exhaust gases such as an oxygen sensor, (O2) for example. An oxygen sensor typically is configured to detect a residual amount of oxygen in the exhaust gases and to send a corresponding signal to the engine control device. The engine control device thus can recognize whether the engine operates under an appropriate air-fuel ratio condition or not.
In some water craft, there are pre O2 sensors and post O2 sensors. The pre O2 sensor detects the residual oxygen at a location adjacent the exhaust manifold and the post O2 sensor detects residual oxygen at a position lower in the exhaust system, closer to the discharge opening of the exhaust system. Typically, the post O2 sensor is located near the point in the exhaust system where the marine engine cooling water mixes with the hot exhaust. New emission standards require the use of a post O2 sensor and require that the O2 sensor remain effective for a pre-determined period of time, which will soon be three (3) years.
The marine industry has had problems getting the post O2 sensor to live in the exhaust stream of a marine engine since it is very close to where the cooling water mixes with the hot exhaust. Today's automotive style marine engines all have some degree of cam overlap. This overlap (intake and exhaust valve open simultaneously) causes a phenomenon known as water reversion at idle speeds. Droplets of water migrate up the exhaust exposing most of the exhaust manifold walls to water. The O2 sensor is a hot ceramic component which is subject to fail when doused with water.